Destroying the bus stations

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<queue>
 6 #define  inf 100000000
 7 using namespace std;
 8 const int N=55;
 9 const int E=20000;
10 int dist[N],del[N][N],vis[N],head[N];
11 bool visit[N];
12 int n,m,k,cnt,ans,u,v,pre[N];
13 struct Node{
14   int v;
15   int next;
16 }edge[E];
17 void init(){
18  memset(head,-1,sizeof(head));
19  memset(visit,0,sizeof(visit));
20  memset(pre,0,sizeof(pre));
21  cnt=0;
22  ans=inf;
23 }
24 void add(int u,int v){
25   edge[cnt].v=v;
26   edge[cnt].next=head[u];
27   head[u]=cnt++;
28 }
29 bool BFS(){
30   for(int i=1;i<=n;i++){
31     dist[i]=inf;
32     vis[i]=false;
33   }
34       queue<int>Q;
35       vis[1]=1;
36       dist[1]=0;
37       Q.push(1);
38      while(!Q.empty()){
39         int u=Q.front();
40         Q.pop();
41         vis[u]=0;
42         for(int i=head[u];i!=-1;i=edge[i].next){
43             int v=edge[i].v;
44             if(!visit[v]&&dist[v]>dist[u]+1){
45                 dist[v]=dist[u]+1;
46                 pre[v]=u;
47                 if(!vis[v]){
48                     Q.push(v);
49                     vis[v]=1;
50                 }
51                 if(v==n&&dist[v]<=k)return true;
52             }
53         }
54      }
55    return false;
56 }
57 void DFS(int depth){
58     if(depth>=ans)return;
59     memset(pre,0,sizeof(pre));
60     if(!BFS()){
61          ans=min(ans,depth);
62          return;
63     }
64     int num=0;
65     for(int i=pre[n];i!=1;i=pre[i]){
66         del[depth][++num]=i;
67     }
68     for(int i=1;i<=num;i++){
69         visit[del[depth][i]]=true;
70         DFS(depth+1);
71         visit[del[depth][i]]=false;
72     }
73 }
74 
75 int main(){
76   while(~scanf("%d%d%d",&n,&m,&k)&&n){
77      init();
78      for(int i=1;i<=m;i++){
79         scanf("%d%d",&u,&v);
80         add(u,v);
81      }
82      DFS(0);
83      printf("%d\n",ans);
84   }
85 }